The present invention relates to a method for preparing fluorescent polymers, and coating compositions containing such fluorescent polymers. In particular, the present method relates to the inclusion of fluorescent compounds in the preparation of polymers useful in coating compositions such that the resultant compositions are detectable by fluorescent means.
A method for preparing a fluorescent polymer is disclosed in U.S. Pat. No. 5,125,929 (Amey). There, a Michael addition reaction produces a linear aminoacid polymer which is fluorescent. In this case, the fluorescence is produced by the polymer backbone. This method is limited by the nature of its chemistry. Moreover, most polymers produced by a Michael addition reaction will not have fluorescence.
U.S. Pat. No. 5,043,406 (Fong) discloses a method for incorporating fluorescent moieties into acrylamide polymers by copolymerizing acrylamide monomers with monomers containing pendant fluorescent moieties. The principal limitation to this method is the lack of commercially available monomers containing pendant fluorescent moieties. Even if other monomers could be modified to incorporate pendant fluorescent moieties, the increased cost of doing so would make the cost of such fluorescent polymers prohibitive.
Both the methods described by Amey and Fong are limited in applicability, either by virtue of the nature of the chemistry involved, or by the lack of available fluorescent starting materials. What is needed is a method for incorporating fluorescence into a broad variety of polymers, thus permitting broader usage of such fluorescent polymers.
A first embodiment of the present invention is directed to a method for preparing a fluorescent polymer, comprising copolymerizing one or more ethylenically unsaturated monomers with a fluorescent compound selected from the group consisting of polynuclear aromatic hydrocarbons and their substituted aromatic derivatives; wherein the resultant polymer contains a fluorescent group.
A second embodiment of the present invention is directed to a coating composition having enhanced UV durability, comprising a fluorescent polymer prepared by copolymerizing an ethylenically unsaturated monomer with a fluorescent compound selected from the group consisting of: polynuclear aromatic hydrocarbons and their substituted aromatic derivatives; and ethylenically unsaturated monomers having pendant fluorescent functionality.
A third embodiment of the present invention is directed to a method for identifying and quantifying the amount, if any, of fluorescent polymer contained in a coating composition, such method comprising the steps of: (a) obtaining a sample of the coating composition or resulting coating to be tested; (b) detecting the fluorescence; and (c) measuring the intensity or the wavelength of the fluorescence of the fluorescent polymer contained in the sample.
As used in this specification, the following terms have the following definitions, unless the context clearly indicates otherwise. xe2x80x9cLatexxe2x80x9d or xe2x80x9clatex compositionxe2x80x9d refers to a dispersion of a water-insoluble polymer which may be prepared by conventional polymerization techniques such as, for example, by emulsion polymerization. xe2x80x9cLatexxe2x80x9d also refers to polymer dispersed in an aqueous composition, wherein the polymer can be prepared directly in the aqueous medium, or first prepared in a non-aqueous medium (e.g., using solution polymerization) and then subsequently dispersed in the aqueous medium. xe2x80x9cFluorescentxe2x80x9d or xe2x80x9cfluorescencexe2x80x9d refers to a compound which, when excited by radiation, occupies a second excited state which is said to xe2x80x9cfluorescexe2x80x9d or emit radiation at a lower energy (longer wavelength) than the original excited state. xe2x80x9cChromophorexe2x80x9d refers to a compound having fluorescence which is capable of being covalently attached to a polymer. xe2x80x9cBackbonexe2x80x9d refers to the main chain of a polymer exclusive of pendant or end groups; xe2x80x9cpendantxe2x80x9d refers to a group suspended from the main chain of a polymer; and xe2x80x9cendxe2x80x9d refers to a group suspended from the end of a polymer chain. xe2x80x9cPVCxe2x80x9d used in reference to paint means pigment volume concentration. The terms xe2x80x9cgroupxe2x80x9d and xe2x80x9cmoietyxe2x80x9d are used interchangeably. The following abbreviations are used: cm=centimeter, mm=millimeters, nm=nanometers, mL=milliliters, HPLC=high pressure liquid chromatography, UV=ultraviolet, ai=active ingredient. Ranges specified are to be read as inclusive, unless specifically identified otherwise.
It has now been discovered that certain weak polymerization inhibitors can be used to incorporate fluorescent moieties into a broad variety of polymers by free radical copolymerization of the polymerization inhibitors with the appropriate monomers. These polymerization inhibitors can be broadly classified as polynuclear aromatic hydrocarbons. Examples of such polynuclear aromatic hydrocarbon clromophores can be found in Russian Patent 478839 (Gladyshev) and xe2x80x9cPolymerization Inhibition by Aromatic Compounds,xe2x80x9d J. Polymer Sci., 52:31 (1961). It has also been found that substituted aromatic derivatives of such polynuclear aromatic hydrocarbons can also be used in this fashion. Such derivatives are those wherein the polynuclear aromatic hydrocarbon is substituted without loss of aromaticity. These substituents include but are not limited to: C1-12 branched or straight chain alkyl or aryl groups optionally substituted with heteroatoms; carboxylic acids and esters thereof; sulfonic acids and derivatives thereof; cyano groups; and halogens. Preferred polynuclear aromatic hydrocarbons include: naphthalene, anthracene, phenanthrene, fluoranthene, acridine, carbazole, pyrene, chrysene, triphenylene, perylene, and their substituted aromatic derivatives. It is especially preferred to use naphthalene, anthracene, phenanthrene, fluoranthene, and their substituted aromatic derivatives. Combinations of chromophores can also be used.
In another embodiment of the present invention, the fluorescent polymers are used as markers for product identification. In this respect, other types of fluorescent polymers can be utilized. For example, such polymers can be prepared by copolymerizing the appropriate monomers with an ethylenically unsaturated monomer having pendant fluorescent functionality.
Detection of the fluorescent polymers is accomplished by taking a sample of the coating composition or the resulting (applied) coating, and analyzing the sample to determine the fluorescence wavelength, and the intensity of the fluorescence emission. HPLC or GPC analysis may be used to determine whether or not the fluorescent moiety is covalently attached to the polymer. (See, for example, S. Sosnowski et al., J. Polvmer Sci., Part A: Polymer Chemistry 32:1497 (1994).) If a sample of the applied coating is used, it may be useful to extract the polymer from the other coating components prior to analysis, in accordance with methods known to those skilled in the art.
Examples of ethylenically unsaturated monomers having pendant fluorescent functionality can be found in: U.S. Pat. No. 5,043,406 (Fong), S. Sosnowski et al., J. Polvmer Sci Part A: Polymer Chemistry 32:1497 (1994), C. L. Zhao et al., Macromolecules, 23:4082 (1990), E. M. Boczar et al., Macromolecules, 26:5772 (1993), M. A. Fox et al., Macromolecules, 23:4533 (1990), and C. Simionescu et al., J. Polymer Sci., 23:2089 (1985). Preferred ethylenically unsaturated monomers having pendant fluorescent functionality include: naphthylmethyl methacrylate, naphthylethyl methacrylate, 9-anthryl methacrylate, 9-anthrylmethyl methacrylate, 2-(9-anthryl)ethyl methacrylate, 1xe2x80x2-(9-anthryl)ethyl methacrylate, 3-hydroxy-2-methylene-3-(1-naphthyl)propionic acid, N-dibenzosuberenyl acrylamide, (9-phenanthryl)methyl methacrylate, and 9-vinyl phenanthrene. It is especially preferred to use naphthylethyl methacrylate, 9-anthryl methacrylate, 3-hydroxy-2-methylene-3-(1-naphthylpropionic acid, (9-phenanthryl)methyl methacrylate, 9-vinyl phenanthrene, or combinations thereof.
Regardless of whether the chromophore being incorporated into the polymer is a polynuclear aromatic hydrocarbon or an ethylenically unsaturated monomer having pendant fluorescent functionality, the method of incorporation is similar. The chromophore is treated as another component in the free radical polymerization process, and is generally added to the monomers at the start of the reaction; however, variations from this procedure are known to those skilled in the art. The polymerization can be conducted in any medium, including aqueous media, polar or non-polar organic solvents, or combinations thereof. Such polymerization techniques are well known to those skilled in the art, and will not be further discussed herein.
The amount of chromophore utilized in the preparation of the fluorescent polymers of the present invention will vary, depending on the type of chromophore and how the chromophore is attached to the resultant polymer (whether it is a pendant or end group, or inserted into the polymer backbone); however, the chromophores will typically be added to the monomer mixture in an amount between 0.001 and 3.0 wt %. It is preferred to add chromophore in an amount between 0.005 and 1.0 wt %, and most preferred to add between 0.01 and 0.5 wt %.
Typical comonomers that are useful in this invention are those that are capable of undergoing free radical polymerization. The choice of comonomer will vary, depending on the choice of chromophore. As used in this specification, the term xe2x80x9cacrylicxe2x80x9d is used in a general sense to describe polymers wherein at least one of the monomers is of the acrylic or methacrylic type, including acrylic and methacrylic acids, esters of acrylic acid or methacrylic acid, and substituted derivatives thereof. xe2x80x9c(Meth)acryl-xe2x80x9d includes both acrylic and methacrylic derivatives. Such monomers are well known in the art. Examples of such acrylic nonomers include: alkyl (meth)acrylates such as methyl methacrylate, ethyl acrylate, methyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, cyclohexyl acrylate, isopropyl acrylate, isobutyl acrylate, n-amyl acrylate, n-propyl acrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, neopentyl acrylate, n-tetradecyl acrylate, n-tetradecyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, n-hexyl methacrylate, isoamyl methacrylate, cyclopentyl methacrylate, n-decyl methacrylate, and the like; other acrylate and methacrylate esters such as 2-bromoethyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-phenylethyl methacrylate, 3-methoxybutyl acrylate, 2-methoxybutyl methacrylate, and 2-n-butoxyethyl methacrylate; active hydrogen-functional monomers including hydroxy-substituted (meth)acrylates such as 2-hydroxyethyl acrylate and 3-hydroxypropyl acrylate; (meth)acryiate including sulfonic acids such as sulfoethyl methacrylate, and sulfopropyl acrylate; and phosphoric acids such as 2-phosphoethyl (meth)acrylate,.
Additional comonomers which can be used in the present invention include: butadiene, styrene, alpha-methyl s tyrene, s odium styrene sulfonate, v inyl toluene, acrylonitrile, methacrylonitrile, alpha-chloroacrylonitrile, ethyl acrylonitrile, methyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, 4-hydroxybutyl vinyl ether, 1,4-butaneglycol divinyl ether, diethyleneglycol divinyl ether, vinyl esters such as vinyl acetate, vinyl versatate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl 2-ethyihexonate and vinyl decanoate; allyl chloride, methallyl chloride, vinylidene chloride, vinyl chloride, vinyl fluoride, vinyldene fluoride, sodium vinyl sulfonaate, butyl vinyl sulfonate, phenyl vinyl sulfone, methyl vinyl sulfone, N-vinyl pyrrolidinone, N-vinyl oxazolidinone, acrolein, acrylamide, methacrylamide, N,N-dime thyl(meth)acrylamide, methylolacrylamide, N-butoxy(meth)acrylamide, isobutoxy(mieth)acrylalmide and the like, allyl triethoxysilane, allyl tris(trimethyls iloxy) silane, 3-acryloxypropyltrimethoxy silane, and the like; other ethylenically unsaturated carboxylic acids and their esters, such as dialkyl and trialkyl esters of di-and tri-carboxylic acids such as itaconic acid and the like, including di(2-ethylhexyl) maleate, dibutyl maleate, dimethyl fumarate, dimethyl itaconate, diethyl citraconate, trimethyl aconitate, diethyl mesaconate, di(2-ethylhexyl) itaconate, di-(2-chloroethyl) itaconate, maleic acid, maleic anhydride, fumaric acid, itaconic acid; and olefins, such as diisobutylene, 1-octene, 1-decene, 1-hexadecene and the like.
These types of monomers are typically polymerized in the presence of water-soluble or oil-soluble initiators. Examples of useful initiators include: persulfates, peroxides, hydroperoxides, percarbonates, per acetates, perbenzoates, azo-functional compounds and other free-radical generating species.
Surfactants are commonly used in emulsion or dispersion polymerization to provide stability, as well as to control particle size. Conventional surfactants include anionic or nonionic emulsifiers or their combination. Typical anionic emulsifiers include but are not limited to: alkali or ammonium alkyl sulfates, alkali or ammonium alkylether sulfates, alkali or ammonium alkylarylether sulfates, alkyl sulfonates, salts of fatty acids, esters of sulfosuccinic acid salts, alkyl diphenylether disulfonates, and salts or free acids of complex organic phosphate esters. Typical nonionic emulsifiers include but are not limited to: polyethers, e.g. ethylene oxide and propylene oxide condensates which include straight and branched chain alkyl and alkylaryl polyethylene glycol and polypropylene glycol ethers and thioethers, alkyl phenoxypoly(ethyleneoxy) ethanols having alkyl groups containing from about 7 to about 18 carbon atoms and having from about 4 to about 100 ethyleneoxy units, and polyoxyalkylene derivatives of hexitol, including sorbitans, sorbides, mannitans, and mannides. Surfactants may be employed in the polymer compositions of the present invention at levels of 0.1-3 wt % or greater, based on the total weight of the final composition.
In preparing the fluorescent polymers of the present invention, any chain-transfer agent, or mixtures thereof, may be used to control molecular weight. Suitable chain transfer agents include, for example, C1-12 alkyl or functional alkyl mercaptans, alkyl or functional alkyl mercaptoalkanoates, or halogenated hydrocarbons, and may be employed in the polymer at levels of 0.01-10 wt %, based on the weight of the polymer.
It is also sometimes useful to increase molecular weight of the resulting polymers. This can be accomplished by addition of ethylenically unsaturated monomer comprising at least two sites of ethylenically unsaturation. Examples of such compounds include: ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, neopentyl glycol dimethacrylate, 1,3-butylene glycol diacrylate, neopentyl glycol diacrylate, trimethylolethane trimethacrylate, dipentaerythritol triacrylate, dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dimethallyl chlorendate, diallyl chlorendate, diallyl fumarate, diallyl itaconate, diallyl phthalate, diallyl isophthalate, triallyl isocyanate, triallyl trimellitate, 1,6-hexanediol diacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, tripropylene glycol diacrylate, allyl methacrylate, and divinyl benzene. Such compounds may be employed in the polymer at levels of 0.01-10 wt %, based on the weight of the polymer.
Other optional components that can be included in this invention include co-solvents, pigments, fillers, dispersants, curing agents, wetting agents, anti-foam agents, UV absorbers, antioxidants, biocides, and stabilizers.
The coating compositions of the present invention can be used to provide coatings on suitable substrates such as wood and reconstituted wood products, concrete, asphalt, fiber cement, stone, marble, clay, plastics (for example, polystyrene, polyethylene, ABS, polyurethane, polyethylene terphthalate, polybutylene terphthalate, polypropylene, polyphenylene, polycarbonate, polyacrylate, polyvinyl chloride, Noryl(copyright), and polysulfone), paper, cardboard, textiles, leather, and metal (ferrous as well as non-ferrous). It has surprisingly been discovered that the inclusion of the fluorescent polymers of the present invention in coating compositions produces in enhanced UV durability of the resultant coatings. The coating compositions of the present invention are therefore preferably used to coat substrates that are routinely subjected to UV light (e.g., outdoor applications).
The coating compositions of the present invention can be applied to desired substrates using conventional application techniques such as conventional or airless spray, roll, brush, curtain, flood, and dip-coating methods. Once applied to the substrate, the coating compositions can be cured at ambient or elevated temperatures.
Films of each test paint were drawn down on Leneta((copyright) 5C we charts using a 3 mil (0.076 mm) Bird(copyright) Film Applicator. The films were allowed to dry for seven days at 25xc2x0 C. and 50% relative humidity. Then initial readings were taken of the 20xc2x0 and 60xc2x0 gloss (the light reflected at angles of 20xc2x0 and 60xc2x0 from the perpendicular) using a Glossgard(copyright) II Glossmeter. The 20xc2x0 and 60xc2x0 gloss readings were repeated after Weather-O-meter(copyright) exposure and reported as a percent retention of the original value. Loss of gloss is a measure of poor durability; thus a higher percent retention indicates better durability.
Films of each test paint were drawn down on aluminum xe2x80x9cQxe2x80x9d panels (Alodine(copyright) 1200S) using a 3 mil (0.076 mm) Bird(copyright) Film Applicator. The films were allowed to dry for seven days at 25xc2x0 C., 50% relative humidity before Weather-O-meter(copyright) exposure. After exposure, a reflectometer was used to measure the Y reflectance of the paint film. The panels were then xe2x80x9csoiledxe2x80x9d using an iron oxide slurry (250 g water, 2 drops of an anionic dispersant, 125 g of iron oxide, well dispersed), air dried three hours and oven dried at 60xc2x0 C. for one hour. After the panels had cooled to room temperature, the paint films were washed under running water using a cheesecloth pad, and air dried for four hours. The reflectometer was used to remeasure the Y-reflectance over the soiled area, which was reported as a percent of the original reading. A higher percent retention indicates cleaner paint films, which indicates better durability.